In the textile industry, fibers are collected and compacted continuously in hoppers for subsequent feeding to a downstream processing machine such as a beater or card.
It is of great importance for further processing that the fiber mat should have a satisfactory regularity; a number of devices and circuits for measurement and consequent control have therefore already been disclosed and are used extensively in the textile industry. Most of these devices comprise a conveying roll, which is preferably of fluted design for the purpose of conveying the fiber efficiently, a plurality of movable contact-pressure noses, so-called pedal noses, and an electrical evaluation device. A device of this kind is described in Walz, "Die moderne Baumwollspinnerei", (Modern Methods of Cotton Spinning), 1960, page 91. German Patent DE No. 3,205,776 shows a further refinement of this method of measurement.
All methods of measurement by means of a roll and a pedal nose to date depend on the trueness of the roll. In this case of fluted rolls, measurement errors additionally occur by reason of the fluting. If measurements over large widths, e.g. 4 m, and precision of the measured values over the width are required, such measurement rolls become very expensive to produce. Accuracies should be within the range of 1/1000 mm. To date it has been impossible to take into account differing sagging behaviors of welding tubes which have been used as such rolls.
It is the object of the invention to provide an improved method of and an inexpensive apparatus for the accurate measurement of the thickness of mats.